gulpfile.js

var gulp = require('gulp');
var sys = require('sys');
var exec = require('child_process').exec;
var hold = false;

gulp.task('phpunit', function() {
    exec('phpunit', function(error, stdout) {
        sys.puts(stdout); 
        hold = false;
    });
}); 

gulp.task('default', function() {
    gulp.watch('**/*.php', function(event) {
        if (!hold) {
            hold = true;
            gulp.run('phpunit');
        }
    });   
});